Targetless vehicular camera calibration method

ABSTRACT

A method of calibrating a vehicular camera includes disposing a camera at a vehicle, moving the vehicle along an arbitrary path, capturing image data with the camera, and processing, via a processor, image data captured by the camera. Responsive to tracking a determined feature across multiple frames of captured image data during movement of the vehicle along the arbitrary path, and responsive to received vehicle data representative of the movement of the vehicle along the arbitrary path, misalignment of the camera is determined. The determined camera misalignment is corrected (i) without use of a target in the field of view of the camera as the vehicle moves along the arbitrary path and (ii) without processing of image data captured by the camera that is representative of a target in the field of view of the camera as the vehicle moves along the arbitrary path.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 15/416,218, filed Jan. 26, 2017, now U.S. Pat. No. 9,979,957, which is a continuation of U.S. patent application Ser. No. 14/282,028, filed May 20, 2014, now U.S. Pat. No. 9,563,951, which claims the filing benefits of U.S. provisional application Ser. No. 61/878,877, filed Sep. 17, 2013, and Ser. No. 61/825,752, filed May 21, 2013, which are hereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to a vehicle vision system for a vehicle and, more particularly, to a vehicle vision system that utilizes one or more cameras at a vehicle.

BACKGROUND OF THE INVENTION

Use of imaging sensors in vehicle imaging systems is common and known. Examples of such known systems are described in U.S. Pat. Nos. 5,949,331; 5,670,935 and/or 5,550,677, which are hereby incorporated herein by reference in their entireties.

SUMMARY OF THE INVENTION

The present invention provides a collision avoidance system or vision system or imaging system for a vehicle that utilizes one or more cameras (such as one or more CMOS cameras) to capture image data representative of images exterior of the vehicle, and provides a calibration system that is operable to determine calibration parameters for the camera or cameras of the vision system without use of fiducial markers or targets in the field of view of the camera or cameras.

The cameras (such as one or more CMOS cameras) capture image data representative of images exterior of the vehicle, and provide the communication/data signals, including camera data or captured image data, that may be displayed at a display screen that is viewable by the driver of the vehicle, such as when the driver is backing up the vehicle, and that may be processed and, responsive to such image processing, the system may detect an object at or near the vehicle and in the path of travel of the vehicle, such as when the vehicle is backing up. The vision system may be operable to display a surround view or bird's eye view of the environment at or around or at least partially surrounding the subject or equipped vehicle, and the displayed image may include a displayed image representation of the subject vehicle.

These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a vehicle with a vision system that incorporates cameras in accordance with the present invention;

FIG. 2 is a schematic showing the coordinate system and angles used to represent the travel of the vehicle during calibration;

FIG. 3 is a perspective view and schematic of the vehicle;

FIG. 4 is a top level flow chart of the targetless software calibration (TSC) algorithm of the present invention;

FIG. 5 is a schematic showing the data acquisition and feature extraction of the system of the present invention;

FIGS. 6A and 6B are flowcharts of the targetless calibration algorithm of the present invention;

FIG. 7 shows details of a structure from motion algorithm or process suitable for use with the system of the present invention;

FIG. 8 shows details of a bundle adjustment process of the system of the present invention;

FIG. 9 shows details of a feature detection algorithm or process of the system of the present invention;

FIG. 10 shows details of an extraction and matching of features process of the system of the present invention;

FIG. 11 shows details of a feature matching process of the system of the present invention;

FIG. 12 is a flow chart of the feature extraction and matching process or algorithm of the system of the present invention; and

FIG. 13 shows details of a feature filtering process of the system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle vision system and/or driver assist system and/or object detection system and/or alert system operates to capture images exterior of the vehicle and may process the captured image data to display images and to detect objects at or near the vehicle and in the predicted path of the vehicle, such as to assist a driver of the vehicle in maneuvering the vehicle in a rearward direction. The vision system includes an image processor or image processing system that is operable to receive image data from one or more cameras and provide an output to a display device for displaying images representative of the captured image data. Optionally, the vision system may provide a top down or bird's eye or surround view display and may provide a displayed image that is representative of the subject vehicle, and optionally with the displayed image being customized to at least partially correspond to the actual subject vehicle.

Referring now to the drawings and the illustrative embodiments depicted therein, a vehicle 10 includes an imaging system or vision system 12 that includes at least one exterior facing imaging sensor or camera, such as a rearward facing imaging sensor or camera 14 a (and the system may optionally include multiple exterior facing imaging sensors or cameras, such as a forwardly facing camera 14 b at the front (or at the windshield) of the vehicle, and a sidewardly/rearwardly facing camera 14 c, 14 d at respective sides of the vehicle), which captures images exterior of the vehicle, with the camera having a lens for focusing images at or onto an imaging array or imaging plane or imager of the camera (FIG. 1). The vision system 12 includes a control or electronic control unit (ECU) or processor 18 that is operable to process image data captured by the cameras and may provide displayed images at a display device 16 for viewing by the driver of the vehicle (although shown in FIG. 1 as being part of or incorporated in or at an interior rearview mirror assembly 20 of the vehicle, the control and/or the display device may be disposed elsewhere at or in the vehicle). The cameras operate to capture frames of image data at a desired or selected frame rate, such as, for example, about 30 frames per second or more or less. The data transfer or signal communication from the camera to the ECU may comprise any suitable data or communication link, such as a vehicle network bus or the like of the equipped vehicle.

The present invention provides a targetless calibration system or targetless software calibration (TSC) for calibrating cameras of a vehicle vision system. The calibration system generates camera calibration parameters, such as translational components: X, Y, Z (mm); and rotational components: Yaw, Pitch, and Roll angles (degrees). No specific vehicle motion required, and the calibration is performed as the vehicle navigates along an arbitrary path. The bundle adjustment may be a core feature of the targetless software calibration, and iteratively refines calibration parameters starting from a known initial estimation. The system uses bundle adjustment (BA) inputs, including image coordinates of matched scene features between two frames of captured image data, vehicle motion vector (V=[S1, S2, ψ]) between two frames of captured image data, an initial estimation of calibration parameters, and/or three dimensional (3D) coordinates of features (such as via a structure from motion algorithm or the like). The vehicle motion vector (V) may be computed using only vehicle CAN Bus data, and may be independent of any image data captured by the camera or cameras of the vehicle.

The system of the present invention thus may provide an algorithm that performs a fast and reliable on-line targetless calibration of one or more cameras installed on a vehicle (in other words, the system estimates camera calibration parameters). The system thus eliminates the need for any camera calibration requiring special setup, such as, for example, a vehicle manufacturer or factory end-of-line process or service or the like.

The conditions for the calibration system include: R_(cal)=(Yaw, Pitch, Roll) and T_(cal)=(X_(cal), Y_(cal), Z_(cal)). The vehicle is moving on the road with arbitrary patterns or texture (in other words, no lane markings or other markings or similar patterns or texturing needed) and along an arbitrary path (with no special maneuvers being needed, such as planned or specific turns or routing, such as driving in a circular loop or the like). The system may utilize a motion model for the camera calibration, such as a kinematic model of vehicle motion of the types described in U.S. patent application Ser. No. 14/282,029, filed May 20, 2014 by James Turk for VEHICLE VISION SYSTEM USING KINEMATIC MODEL OF VEHICLE MOTION, and published Nov. 27, 2014 as U.S. Publication No. US-2014-0350834, and U.S. provisional application Ser. No. 61/825,753, filed May 21, 2013, which are hereby incorporated herein by reference in their entireties.

Thus, and as can be seen with reference to FIGS. 5-8, the system receives image data from a camera or cameras of the vehicle and extracts and matches features over multiple images or frames of captured image data. The system also receives data from a kinematic model of vehicle motion (such as a kinematic model of vehicle motion of the types described in U.S. patent application Ser. No. 14/282,029, filed May 20, 2014 by James Turk for VEHICLE VISION SYSTEM USING KINEMATIC MODEL OF VEHICLE MOTION, and published Nov. 27, 2014 as U.S. Publication No. US-2014-0350834, and U.S. provisional application Ser. No. 61/825,753, filed May 21, 2013, which are hereby incorporated herein by reference in their entireties), and determines the vehicle motion between frames and, based on initial parameter estimations and camera intrinsic parameters, the system determines the calibration parameters for the camera.

The targetless software calibration system of the present invention uses software modules such as an interface software module (which provides an image input or image data input and/or a network input or CAN input to the system) and a kinematic model input. The system uses image processing to provide feature detection, feature extraction, feature matching and feature filtering, and uses computer vision to provide a calibration parameters setup, structure-from-motion, a bundle adjustment, and an averaging of calibration results. For example, and as shown in FIG. 12, the system uses feature detection (FIG. 9), and extracts and matches feature descriptors (FIG. 10) and creates feature matches (FIG. 11), and outputs a list of valid features and their movements or movement patterns. The feature filtering (FIG. 13) enhances the structure-from-motion and bundle adjustment by eliminating feature pairs that do not satisfy the established rules for valid feature pairs in valid frame pairs.

As shown in FIG. 9, the feature detection may detect features within an image frame. The system thus may detect N features (such as three features shown in FIG. 9) in three separate rectangular constant image ROIs, with the detection occurring periodically, such as every K frames (such as every frame or every other frame or every third frame or the like). The feature detection may utilize various detection methods, such as a Harris corner detector, speeded-up robust features (SURF), minimum eigenvalue and/or the like. The input may comprise a sequence of images with the ROI locations and dimensions, which may be constant for each image in the sequence. The output may comprise a list of pixel coordinates for each detected feature in each image frame.

As shown in FIG. 10, the system may utilize extraction and matching of feature descriptors. For each detected feature in each image of the sequence of images, the system may build a descriptor, an m-dimensional vector, based on the image information in the neighborhood of the feature. The system may match the descriptor based on the distance d_(ij) from each other in frames i and j. The input may comprise image coordinates of the detected features in each image and the output may comprise a descriptor for each features, a list of matched features and a match metric.

Thus, the present invention provides a targetless camera calibration system that is operable to calibrate the cameras during any normal driving movement of the vehicle equipped with the cameras and calibrated systems. The system algorithm, when the system is calibrating more than one camera of the vehicle, does not use overlap image areas between the cameras. The system may calibrate the cameras when the vehicle and/or camera(s) undergo any movement in six degrees of freedom (such as translational movements (x, y, z) forward/backward, side to side, up/down, and such as rotational movements pitch, yaw, roll). The system achieves the calibration by matching features over multiple captured images and determining how the features position or location in the captured images may be different from where they would be with a properly calibrated camera, based at least in part on an input of a kinematic model of the actual vehicle movement.

Various vehicle camera calibration systems have been proposed, such as those described in U.S. Pat. Nos. 8,421,865; 7,914,187 and/or 7,949,486, and/or PCT Application No. PCT/US2011/036967, filed May 18, 2011, and/or PCT Application No. PCT/CA2012/000378, filed Apr. 25, 2012, and/or PCT Application No. PCT/US2012/064980, filed Nov. 14, 2012, which are all hereby incorporated herein by reference in their entireties. Such systems typically use and rely on a reference element on the vehicle itself. For outside viewing cameras (such as a side camera disposed at or in an exterior rearview mirror of the vehicle), the vehicle manufacturer may initially calibrate the camera in the vehicle assembly plant, where the system is trained or set to correctly display on the screen what is actually occurring or existing in real life on the ground at or near the vehicle. If nothing changes over time, the system will continue to work properly. But over time, things change (for example, the exterior mirror may be moved in any of six degrees of freedom, such as along the x, y and z directions and/or about three rotational axes), and the camera follows any changes in the mirror so that what is shown on the display screen may no longer be true to the actual outside scene or reality. With multiple cameras, this may become critical if one camera is out of sync with other cameras. While use of a reference point works to calibrate the cameras, the reference point may also be changed on the vehicle.

The system of the present invention calibrates the cameras of the vehicle multi-camera system without use of reference points on the vehicle. The system figures out that a camera is out of calibration and then figures out how to calibrate it, all while the vehicle is being normally driven by the driver.

While the vehicle is driven along a road, the cameras capture frames of image data, and the system identifies or tags features in the captured images (such as, for example, a tree or a mailbox or a sign or the like) and then over a set of frames the system matches the features to determine how they are moving in the captured image and relative to the vehicle movement. The system receives an input from a kinematic model that provides kinematic data that indicates exactly how the vehicle is moving in reality. The control of the system thus knows how the vehicle moved in reality (over the period of time that the frames were captured) and knows how the determined and matched features have moved as the camera has seen them (over the period of time that the frames were captured), and thus the control sees how and where the features are moving on the image plane itself. Thus, the system knows that for a given real movement of the vehicle (such as based on a kinematic model), a determined feature in the camera's field of view should move in a particular manner and should appear at a particular location at a particular time or amount of movement of the vehicle (such as in a successive captured image or frame of image data). When the system determines that a feature is not where it is expected to be, the system can determine that the camera is out of calibration or misaligned, and can adjust the camera and/or image processing and/or display characteristics accordingly.

The system may also determine if the object is also moving, in order to avoid a false determination of camera misalignment when the object is moving as well as the vehicle and not with the vehicle (and thus does not appear where it is expected to be). For example, with a multi-camera system, two cameras may capture images of the object, and the system may determine whether or not the object is moving by comparing the image data captured by the two cameras. With the system determining that the object is stationary (such as by seeing that the “movement” of the object in the captured image data, such as due to the vehicle movement, is the generally the same between the two sets of multiple frames of captured image data), the system can then determine whether one of the two cameras is misaligned, as discussed above.

Thus, the targetless calibration system of the present invention is operable to calibrate a camera or cameras of a vehicle without use of reference points on or off the vehicle. The output of the calibration process is an exact or substantially exact location and orientation of the camera with respect to vehicle coordinate system (whereas known systems may calculate a transform function and use a corresponding look-up table to generate a transfer map between the raw image data and display screen). The system of the present invention has no constraints on the driving maneuvers of the vehicle (in other words, the driver is not required to drive in a straight line for a period of time during calibration), and the system is operable to determine the calibration of the cameras during any driving maneuvers of the vehicle.

Also, if the vehicle is driven in straight line only, then only four degrees of freedom of the camera can be calibrated, namely the three rotational axes (pitch, yaw and roll) and the camera height. Such straight line driving constraints are unnatural constraints on driving. However, with the present invention, the vehicle may be driven in a normal manner, with turns involved. When the vehicle is driven naturally, with turns involved, then all six degrees of freedom of the camera can be checked and calibrated (so the location and orientation of the camera can be determined). The calibration time is shortened by the system of the present invention because no time is wasted when the vehicle turns naturally as the calibration process is not suspended for the duration of the turn.

The camera or sensor may comprise any suitable camera or sensor. Optionally, the camera may comprise a “smart camera” that includes the imaging sensor array and associated circuitry and image processing circuitry and electrical connectors and the like as part of a camera module, such as by utilizing aspects of the vision systems described in International Publication Nos. WO 2013/081984 and/or WO 2013/081985, which are hereby incorporated herein by reference in their entireties.

The system includes an image processor operable to process image data captured by the camera or cameras, such as for detecting objects or other vehicles or pedestrians or the like in the field of view of one or more of the cameras. For example, the image processor may comprise an EyeQ2 or EyeQ3 image processing chip available from Mobileye Vision Technologies Ltd. of Jerusalem, Israel, and may include object detection software (such as the types described in U.S. Pat. Nos. 7,855,755; 7,720,580 and/or 7,038,577, which are hereby incorporated herein by reference in their entireties), and may analyze image data to detect vehicles and/or other objects. Responsive to such image processing, and when an object or other vehicle is detected, the system may generate an alert to the driver of the vehicle and/or may generate an overlay at the displayed image to highlight or enhance display of the detected object or vehicle, in order to enhance the driver's awareness of the detected object or vehicle or hazardous condition during a driving maneuver of the equipped vehicle.

The vehicle may include any type of sensor or sensors, such as imaging sensors or radar sensors or lidar sensors or ladar sensors or ultrasonic sensors or the like. The imaging sensor or camera may capture image data for image processing and may comprise any suitable camera or sensing device, such as, for example, a two dimensional array of a plurality of photosensor elements arranged in at least 640 columns and 480 rows (at least a 640×480 imaging array, such as a megapixel imaging array or the like), with a respective lens focusing images onto respective portions of the array. The photosensor array may comprise a plurality of photosensor elements arranged in a photosensor array having rows and columns. Preferably, the imaging array has at least 300,000 photosensor elements or pixels, more preferably at least 500,000 photosensor elements or pixels and more preferably at least 1 million photosensor elements or pixels. The imaging array may capture color image data, such as via spectral filtering at the array, such as via an RGB (red, green and blue) filter or via a red/red complement filter or such as via an RCC (red, clear, clear) filter or the like. The logic and control circuit of the imaging sensor may function in any known manner, and the image processing and algorithmic processing may comprise any suitable means for processing the images and/or image data.

For example, the vision system and/or processing and/or camera and/or circuitry may utilize aspects described in U.S. Pat. Nos. 7,005,974; 5,760,962; 5,877,897; 5,796,094; 5,949,331; 6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202; 6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452; 6,822,563; 6,891,563; 6,946,978; 7,859,565; 5,550,677; 5,670,935; 6,636,258; 7,145,519; 7,161,616; 7,230,640; 7,248,283; 7,295,229; 7,301,466; 7,592,928; 7,881,496; 7,720,580; 7,038,577; 6,882,287; 5,929,786 and/or 5,786,772, and/or International Publication Nos. 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No. 61/844,630, filed Jul. 10, 2013; Ser. No. 61/844,173, filed Jul. 9, 2013; Ser. No. 61/844,171, filed Jul. 9, 2013; Ser. No. 61/842,644, filed Jul. 3, 2013; Ser. No. 61/840,542, filed Jun. 28, 2013; Ser. No. 61/838,619, filed Jun. 24, 2013; Ser. No. 61/838,621, filed Jun. 24, 2013; Ser. No. 61/837,955, filed Jun. 21, 2013; Ser. No. 61/836,900, filed Jun. 19, 2013; Ser. No. 61/836,380, filed Jun. 18, 2013; Ser. No. 61/833,080, filed Jun. 10, 2013; Ser. No. 61/830,375, filed Jun. 3, 2013; Ser. No. 61/830,377, filed Jun. 3, 2013; Ser. No. 61/823,648, filed May 15, 2013; Ser. No. 61/823,644, filed May 15, 2013; Ser. No. 61/821,922, filed May 10, 2013; Ser. No. 61/819,835, filed May 6, 2013; Ser. No. 61/819,033, filed May 3, 2013; Ser. No. 61/816,956, filed Apr. 29, 2013; Ser. No. 61/815,044, filed Apr. 23, 2013; and/or Ser. No. 61/813,361, filed Apr. 18, 2013, which are all hereby incorporated herein by reference in their entireties. The system may communicate with other communication systems via any suitable means, such as by utilizing aspects of the systems described in International Publication Nos. WO/2010/144900; WO 2013/043661 and/or WO 2013/081985, and/or U.S. patent application Ser. No. 13/202,005, filed Aug. 17, 2011, now U.S. Pat. No. 9,126,525, which are hereby incorporated herein by reference in their entireties.

The imaging device and control and image processor and any associated illumination source, if applicable, may comprise any suitable components, and may utilize aspects of the cameras and vision systems described in U.S. Pat. Nos. 5,550,677; 5,877,897; 6,498,620; 5,670,935; 5,796,094; 6,396,397; 6,806,452; 6,690,268; 7,005,974; 7,937,667; 7,123,168; 7,004,606; 6,946,978; 7,038,577; 6,353,392; 6,320,176; 6,313,454 and/or 6,824,281, and/or International Publication Nos. WO 2010/099416; WO 2011/028686 and/or WO 2013/016409, and/or U.S. Pat. Publication No. US 2010-0020170, and/or U.S. patent application Ser. No. 13/534,657, filed Jun. 27, 2012, and published Jan. 3, 2013 as U.S. Publication No. US-2013-0002873, which are all hereby incorporated herein by reference in their entireties. The camera or cameras may comprise any suitable cameras or imaging sensors or camera modules, and may utilize aspects of the cameras or sensors described in U.S. Publication No. US-2009-0244361 and/or U.S. patent application Ser. No. 13/260,400, filed Sep. 26, 2011, now U.S. Pat. No. 8,542,451, and/or U.S. Pat. Nos. 7,965,336 and/or 7,480,149, which are hereby incorporated herein by reference in their entireties. The imaging array sensor may comprise any suitable sensor, and may utilize various imaging sensors or imaging array sensors or cameras or the like, such as a CMOS imaging array sensor, a CCD sensor or other sensors or the like, such as the types described in U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962; 5,715,093; 5,877,897; 6,922,292; 6,757,109; 6,717,610; 6,590,719; 6,201,642; 6,498,620; 5,796,094; 6,097,023; 6,320,176; 6,559,435; 6,831,261; 6,806,452; 6,396,397; 6,822,563; 6,946,978; 7,339,149; 7,038,577; 7,004,606; 7,720,580 and/or 7,965,336, and/or International Publication Nos. WO/2009/036176 and/or WO/2009/046268, which are all hereby incorporated herein by reference in their entireties.

The camera module and circuit chip or board and imaging sensor may be implemented and operated in connection with various vehicular vision-based systems, and/or may be operable utilizing the principles of such other vehicular systems, such as a vehicle headlamp control system, such as the type disclosed in U.S. Pat. Nos. 5,796,094; 6,097,023; 6,320,176; 6,559,435; 6,831,261; 7,004,606; 7,339,149 and/or 7,526,103, which are all hereby incorporated herein by reference in their entireties, a rain sensor, such as the types disclosed in commonly assigned U.S. Pat. Nos. 6,353,392; 6,313,454; 6,320,176 and/or 7,480,149, which are hereby incorporated herein by reference in their entireties, a vehicle vision system, such as a forwardly, sidewardly or rearwardly directed vehicle vision system utilizing principles disclosed in U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962; 5,877,897; 5,949,331; 6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202; 6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452; 6,822,563; 6,891,563; 6,946,978 and/or 7,859,565, which are all hereby incorporated herein by reference in their entireties, a trailer hitching aid or tow check system, such as the type disclosed in U.S. Pat. No. 7,005,974, which is hereby incorporated herein by reference in its entirety, a reverse or sideward imaging system, such as for a lane change assistance system or lane departure warning system or for a blind spot or object detection system, such as imaging or detection systems of the types disclosed in U.S. Pat. Nos. 7,881,496; 7,720,580; 7,038,577; 5,929,786 and/or 5,786,772, and/or U.S. provisional applications, Ser. No. 60/628,709, filed Nov. 17, 2004; Ser. No. 60/614,644, filed Sep. 30, 2004; Ser. No. 60/618,686, filed Oct. 14, 2004; Ser. No. 60/638,687, filed Dec. 23, 2004, which are hereby incorporated herein by reference in their entireties, a video device for internal cabin surveillance and/or video telephone function, such as disclosed in U.S. Pat. Nos. 5,760,962; 5,877,897; 6,690,268 and/or 7,370,983, and/or U.S. Publication No. US-2006-0050018, which are hereby incorporated herein by reference in their entireties, a traffic sign recognition system, a system for determining a distance to a leading or trailing vehicle or object, such as a system utilizing the principles disclosed in U.S. Pat. Nos. 6,396,397 and/or 7,123,168, which are hereby incorporated herein by reference in their entireties, and/or the like.

Optionally, the circuit board or chip may include circuitry for the imaging array sensor and or other electronic accessories or features, such as by utilizing compass-on-a-chip or EC driver-on-a-chip technology and aspects such as described in U.S. Pat. No. 7,255,451 and/or U.S. Pat. No. 7,480,149; and/or U.S. Publication No. US-2006-0061008 and/or U.S. patent application Ser. No. 12/578,732, filed Oct. 14, 2009, now U.S. Pat. No. 9,487,144, which are hereby incorporated herein by reference in their entireties.

Optionally, the vision system may include a display for displaying images captured by one or more of the imaging sensors for viewing by the driver of the vehicle while the driver is normally operating the vehicle. Optionally, for example, the vision system may include a video display device disposed at or in the interior rearview mirror assembly of the vehicle, such as by utilizing aspects of the video mirror display systems described in U.S. Pat. No. 6,690,268 and/or U.S. patent application Ser. No. 13/333,337, filed Dec. 21, 2011, now U.S. Pat. No. 9,264,672, which are hereby incorporated herein by reference in their entireties. The video mirror display may comprise any suitable devices and systems and optionally may utilize aspects of the compass display systems described in U.S. Pat. Nos. 7,370,983; 7,329,013; 7,308,341; 7,289,037; 7,249,860; 7,004,593; 4,546,551; 5,699,044; 4,953,305; 5,576,687; 5,632,092; 5,677,851; 5,708,410; 5,737,226; 5,802,727; 5,878,370; 6,087,953; 6,173,508; 6,222,460; 6,513,252 and/or 6,642,851, and/or European patent application, published Oct. 11, 2000 under Publication No. EP 0 1043566, and/or U.S. Publication No. US-2006-0061008, which are all hereby incorporated herein by reference in their entireties. Optionally, the video mirror display screen or device may be operable to display images captured by a rearward viewing camera of the vehicle during a reversing maneuver of the vehicle (such as responsive to the vehicle gear actuator being placed in a reverse gear position or the like) to assist the driver in backing up the vehicle, and optionally may be operable to display the compass heading or directional heading character or icon when the vehicle is not undertaking a reversing maneuver, such as when the vehicle is being driven in a forward direction along a road (such as by utilizing aspects of the display system described in International Publication No. WO 2012/051500, which is hereby incorporated herein by reference in its entirety).

Optionally, the vision system (utilizing the forward facing camera and a rearward facing camera and other cameras disposed at the vehicle with exterior fields of view) may be part of or may provide a display of a top-down view or birds-eye view system of the vehicle or a surround view at the vehicle, such as by utilizing aspects of the vision systems described in International Publication Nos. WO 2010/099416; WO 2011/028686; WO 2012/075250; WO 2013/019795; WO 2012/075250; WO 2012/145822; WO 2013/081985; WO 2013/086249 and/or WO 2013/109869, and/or U.S. patent application Ser. No. 13/333,337, filed Dec. 21, 2011, now U.S. Pat. No. 9,264,672, which are hereby incorporated herein by reference in their entireties.

Optionally, a video mirror display may be disposed rearward of and behind the reflective element assembly and may comprise a display such as the types disclosed in U.S. Pat. Nos. 5,530,240; 6,329,925; 7,855,755; 7,626,749; 7,581,859; 7,446,650; 7,370,983; 7,338,177; 7,274,501; 7,255,451; 7,195,381; 7,184,190; 5,668,663; 5,724,187 and/or 6,690,268, and/or in U.S. Publication Nos. US-2006-0061008 and/or US-2006-0050018, which are all hereby incorporated herein by reference in their entireties. The display is viewable through the reflective element when the display is activated to display information. The display element may be any type of display element, such as a vacuum fluorescent (VF) display element, a light emitting diode (LED) display element, such as an organic light emitting diode (OLED) or an inorganic light emitting diode, an electroluminescent (EL) display element, a liquid crystal display (LCD) element, a video screen display element or backlit thin film transistor (TFT) display element or the like, and may be operable to display various information (as discrete characters, icons or the like, or in a multi-pixel manner) to the driver of the vehicle, such as passenger side inflatable restraint (PSIR) information, tire pressure status, and/or the like. The mirror assembly and/or display may utilize aspects described in U.S. Pat. Nos. 7,184,190; 7,255,451; 7,446,924 and/or 7,338,177, which are all hereby incorporated herein by reference in their entireties. The thicknesses and materials of the coatings on the substrates of the reflective element may be selected to provide a desired color or tint to the mirror reflective element, such as a blue colored reflector, such as is known in the art and such as described in U.S. Pat. Nos. 5,910,854; 6,420,036 and/or 7,274,501, which are hereby incorporated herein by reference in their entireties.

Optionally, the display or displays and any associated user inputs may be associated with various accessories or systems, such as, for example, a tire pressure monitoring system or a passenger air bag status or a garage door opening system or a telematics system or any other accessory or system of the mirror assembly or of the vehicle or of an accessory module or console of the vehicle, such as an accessory module or console of the types described in U.S. Pat. Nos. 7,289,037; 6,877,888; 6,824,281; 6,690,268; 6,672,744; 6,386,742 and/or 6,124,886, and/or U.S. Publication No. US-2006-0050018, which are hereby incorporated herein by reference in their entireties.

Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents. 

1. A method of calibrating a vehicular camera, said method comprising: disposing a camera at a vehicle so as to have a field of view exterior of the vehicle, wherein the camera comprises a two-dimensional photosensor array having a plurality of photosensing elements; moving the vehicle along an arbitrary path; capturing image data with the camera as the vehicle moves along the arbitrary path; processing, via a processor, image data captured by the camera; receiving at the processor vehicle data representative of vehicle kinematic motion as the vehicle moves along the arbitrary path; responsive to processing by the processor of multiple frames of image data captured by the camera as the vehicle moves along the arbitrary path, determining at least one feature present in the multiple frames of image data captured by the camera and tracking the determined at least one feature across the multiple frames of image data captured by the camera; responsive to tracking the determined at least one feature across the multiple frames of image data captured by the camera during movement of the vehicle along the arbitrary path, and responsive to the received vehicle data representative of the movement of the vehicle along the arbitrary path, determining misalignment of the camera in one or more of (i) its yaw angle, (ii) its pitch angle and (iii) its roll angle; correcting the determined misalignment of the camera; wherein correcting the determined misalignment of the camera starts from at least one of (i) an initial estimation of camera calibration and (ii) an intrinsic parameter of the camera; and wherein correcting the determined misalignment of the camera is achieved (i) without use of a target in the field of view of the camera as the vehicle moves along the arbitrary path and (ii) without processing of image data captured by the camera that is representative of a target in the field of view of the camera as the vehicle moves along the arbitrary path.
 2. The method of claim 1, wherein the camera is one of a plurality of cameras disposed at the vehicle, each having a respective field of view exterior of the vehicle, and wherein image data captured by at least some cameras of the plurality of cameras is for use by a surround view system of the vehicle.
 3. The method of claim 2, wherein correcting the determined misalignment of the camera comprises correcting the determined misalignment of each camera of the plurality of cameras (i) without use of a target in the respective fields of view of the cameras as the vehicle moves along the arbitrary path and (ii) without processing of image data captured by the cameras that is representative of a target in the respective fields of views of the cameras as the vehicle moves along the arbitrary path.
 4. The method of claim 2, wherein the camera is disposed at a driver side of the vehicle, and wherein another camera of the plurality of cameras comprises a camera disposed at a rear portion of the vehicle, and wherein another camera of the plurality of camera cameras comprises a passenger side camera disposed at a passenger side of the vehicle.
 5. The method of claim 4, wherein the camera is disposed at a driver-side exterior rearview mirror assembly of the vehicle, and wherein the passenger side camera is disposed at a passenger-side exterior rearview mirror assembly of the vehicle.
 6. The method of claim 4, wherein each camera of the plurality of cameras comprises a two-dimensional CMOS photosensor array comprising a plurality of photosensing elements.
 7. The method of claim 2, wherein the surround view system of the vehicle provides a bird's eye view of the environment at or around or at least partially surrounding the vehicle.
 8. The method of claim 1, comprising generating camera calibration parameters at least in part by refining calibration parameters starting from an initial estimation of camera calibration.
 9. The method of claim 1, comprising generating camera calibration parameters at least in part by refining calibration parameters starting from an intrinsic parameter of the camera.
 10. The method of claim 1, wherein processing by the processor of image data captured by the camera provides at least one of (i) feature detection, (ii) feature extraction, (iii) feature matching and (iv) feature filtering.
 11. The method of claim 1, wherein processing by the processor of image data captured by the camera eliminates feature pairs that do not satisfy established rules for valid feature pairs in valid frame pairs.
 12. The method of claim 1, wherein correcting the determined misalignment of the camera utilizes, at least in part, structure-from-motion during processing of image data captured by the camera as the vehicle moves along the arbitrary path.
 13. The method of claim 1, wherein correcting the determined misalignment of the camera utilizes, at least in part, tracking of feature descriptors during processing of image data captured by the camera as the vehicle moves along the arbitrary path.
 14. The method of claim 1, wherein correcting the determined misalignment of the camera is achieved without use of reference points on the vehicle.
 15. The method of claim 1, wherein the vehicle data comprises at least one of (i) data related to steering of the vehicle and (ii) data related to speed of the vehicle.
 16. The method of claim 15, wherein the vehicle data is carried by a communication bus system of the vehicle.
 17. The method of claim 16, wherein the communication bus system comprises a CAN system.
 18. The method of claim 1, wherein moving the vehicle along the arbitrary path comprises moving the vehicle along an assembly line at a vehicle manufacturer.
 19. The method of claim 1, wherein moving the vehicle along the arbitrary path comprises moving the vehicle along a road being traveled by the vehicle.
 20. The method of claim 19, wherein the determined at least one feature comprises a sign at the road being traveled by the vehicle.
 21. The method of claim 19, wherein the determined at least one feature comprises a mailbox at the road being traveled by the vehicle.
 22. The method of claim 19, wherein the determined at least one feature comprises a tree at the road being traveled by the vehicle.
 23. A method of calibrating a vehicular camera, said method comprising: disposing a camera at a vehicle so as to have a field of view exterior of the vehicle, wherein the camera comprises a two-dimensional photosensor array having a plurality of photosensing elements; moving the vehicle along an arbitrary path; capturing image data with the camera as the vehicle moves along the arbitrary path; processing, via a processor, image data captured by the camera; receiving at the processor vehicle data representative of vehicle kinematic motion as the vehicle moves along the arbitrary path, wherein the vehicle data comprises vehicle steering data and vehicle speed data; responsive to processing by the processor of multiple frames of image data captured by the camera as the vehicle moves along the arbitrary path, determining at least one feature present in the multiple frames of image data captured by the camera and tracking the determined at least one feature across the multiple frames of image data captured by the camera; responsive to tracking the determined at least one feature across the multiple frames of image data captured by the camera during movement of the vehicle along the arbitrary path, and responsive to the received vehicle data representative of the movement of the vehicle along the arbitrary path, determining misalignment of the camera in one or more of (i) its yaw angle, (ii) its pitch angle and (iii) its roll angle; correcting the determined misalignment of the camera; wherein correcting the determined misalignment of the camera starts from an intrinsic parameter of the camera; and wherein correcting the determined misalignment of the camera is achieved (i) without use of a target in the field of view of the camera as the vehicle moves along the arbitrary path and (ii) without processing of image data captured by the camera that is representative of a target in the field of view of the camera as the vehicle moves along the arbitrary path.
 24. The method of claim 23, wherein the camera is one of a plurality of cameras disposed at the vehicle, each having a respective field of view exterior of the vehicle, and wherein image data captured by at least some cameras of the plurality of cameras is for use by a surround view system of the vehicle.
 25. The method of claim 23, wherein moving the vehicle along the arbitrary path comprises moving the vehicle along an assembly line at a vehicle manufacturer.
 26. The method of claim 23, wherein moving the vehicle along the arbitrary path comprises moving the vehicle along a road being traveled by the vehicle.
 27. The method of claim 23, wherein the vehicle data is carried by a communication bus system of the vehicle.
 28. The method of claim 27, wherein the communication bus system comprises a CAN system.
 29. A method of calibrating a vehicular camera, said method comprising: providing a plurality of cameras, the plurality of cameras comprising a driver-side camera, a passenger-side camera and a rear camera; disposing the driver-side camera at a driver side of the vehicle so as to have a field of view exterior and sideward of the vehicle; disposing the passenger-side camera at a passenger side of the vehicle so as to have a field of view exterior and sideward of the vehicle; disposing the rear camera at a rear side of the vehicle so as to have a field of view exterior and rearward of the vehicle; wherein each of the cameras comprises a two-dimensional photosensor array having a plurality of photosensing elements; moving the vehicle along an arbitrary path, wherein moving the vehicle along the arbitrary path comprises moving the vehicle along an assembly line at a vehicle manufacturer; capturing image data with the cameras as the vehicle moves along the arbitrary path; processing, via a processor, image data captured by the cameras; receiving at the processor vehicle data representative of vehicle kinematic motion as the vehicle moves along the arbitrary path; responsive to processing by the processor of multiple frames of image data captured by the cameras as the vehicle moves along the arbitrary path, determining at least one feature present in the multiple frames of image data captured by a respective camera of the cameras and tracking the determined at least one feature across the multiple frames of image data captured by the respective camera of the cameras; responsive to tracking the determined at least one feature across the multiple frames of image data captured by the respective camera of the cameras during movement of the vehicle along the arbitrary path, and responsive to the received vehicle data representative of the movement of the vehicle along the arbitrary path, determining misalignment of the respective camera of the cameras in one or more of (i) its yaw angle, (ii) its pitch angle and (iii) its roll angle; correcting the determined misalignment of the respective camera of the cameras; and wherein correcting the determined misalignment of the respective camera of the cameras is achieved (i) without use of a target in the respective field of view of the respective camera as the vehicle moves along the arbitrary path and (ii) without processing of image data representative of a target in the respective field of view of respective camera as the vehicle moves along the arbitrary path.
 30. The method of claim 29, wherein correcting the determined misalignment of the respective camera of the cameras starts from an intrinsic parameter of the respective camera.
 31. The method of claim 29, wherein correcting the determined misalignment of the respective camera of the cameras starts from an initial estimation of camera calibration of the respective camera.
 32. The method of claim 29, wherein the driver-side camera is disposed at a driver-side exterior rearview mirror assembly of the vehicle, and wherein the passenger-side camera is disposed at a passenger-side exterior rearview mirror assembly of the vehicle.
 33. The method of claim 29, wherein each camera of the plurality of cameras comprises a two-dimensional CMOS photosensor array comprising a plurality of photosensing elements.
 34. The method of claim 33, wherein the vehicle data comprises vehicle speed data.
 35. The method of claim 34, wherein the vehicle data comprises vehicle steering data.
 36. The method of claim 29, wherein image data captured by at least some cameras of the plurality of cameras is for use by a surround view system of the vehicle.
 37. The method of claim 36, wherein the surround view system of the vehicle provides a bird's eye view of the environment at or around or at least partially surrounding the vehicle. 